Mantle plume formation away from the LLSVPs

Formation of mantle plumes is often linked to the large low-shear-velocity provinces (LLSVPs) along the core-mantle boundary (CMB) evidenced by their strong spatial associations. However, a small portion of mantle plumes lie far from the major Pacific and African LLSVPs, and their formation cannot be explained by the classical models. Geophysical observations reveal that a few mantle plumes locate nearby the high seismic velocity anamolies (e.g., slab graveyard) along the CMB, indicating the influence of the subduction slabs on plume generation. In this study, we propose that the heterogenous accumulation of subduction slabs along the CMB may facilitate plume generation.

To test this hypothesis, we established a thermo-mechanically coupled numerical model. The model incorporated variations in slab distribution along the CMB to simulate slab graveyard heterogeneity and tracked the distribution of chemical components. The key results are: (1) In the models with heterogenous distribution of subduction slabs along the CMB, mantle plumes are formed induced by the lateral sliding of the heavy subduction slabs. This process is driven by gravity-induced migration and convergence of low-viscosity, high-buoyancy thermo-chemical material in the thermal boundary layer, which generates local thermal-buoyancy anomalies. (2) In the models with homogeneous distribution of subduction slabs or no subduction slabs, mantle plumes failed to form. (3) The initiation rate of mantle plumes correlates positively with slab accumulation height variations and thermal boundary layer thickness; conversely, a higher proportion of dense chemical components in the slab graveyard suppresses plume initiation.

Our modeling results may provide new insights on mantle plume formation away from the LLSVPs along the CMB, which could explain the observed mantle plumes that locate far from the LLSVPs in the present day.